American president's undergarment (5)
I believe the answer is:
teddy
I believe this clue is a double definition.
'american president's' is the first definition.
(Theodore Roosevelt)
'undergarment' is the second definition.
(all-in-one undergarment)
(Other definitions for teddy that I've seen before include "Stuffed bear" , "Child's soft toy" , "Stuffed toy" , "Type of bear" , "plaything" .)